Since the appearance of the first antibiotic-resistant bacterial strains in the 1940's, at least thirteen strains that are impervious to many antibiotics have been discovered. According to the Infectious Disease Society of America, bacteria that are resistant to one or more drugs are responsible for some 100,000 U.S. hospital deaths a year, and cost the health care system more than $34 billion. The discovery of new antibiotics, especially those that act via the inhibition of a novel target, is an urgent need.